Our overall objective is to investigate active and passive immunity against malaria, with the main emphasis on sporozoite-induced protection. The fact that extensive and consistant protection of rodents has been obtained by immunization with X-irradiated sporozoites, and that a reasonable degree of sporozoite purification has been achieved, supports our choice of experimental model for investigating the mechanism of this protection. The present emphasis will be on cell- mediated phenomena in the sporozoite-induced immune response, and their interaction with humoral factors. This will be pursued by: 1) Determining the effects of depletion of thymus dependent lymphocytes (T cell) on the acquisition of protective immunity and production of anti- sporozoite antibodies (CSP and SNA). 2) Determining if resistance can be adoptively transferred with immune lymphoid cells. 3) Determining if immune animals will elicit delayed-type hypersensitivity (DTH) reaction in response to intradermal injections of sporozoite antigens. 4) Studying the formation of granulomas, observed in the livers of immunized animals and its relationship to the development of protective immunity. Investigations on the nature of the interaction between sporozoites and immune as well as normal serum will be continued. As a further long range goal we also plan to define some of the basic alterations of the immune system in malaria. This will be approached by: 1) Investigating the nature of the cellular alterations of the lymphoid system in rodent malaria. 2) Characterizing the alterations of serum complement in malaria and the mechanisms which lead to these changes.